Methods for producing polyisoprene latex dispersions

This application is a National-Stage application of PCT/US2021/037282 filed on Jun. 14, 2021, which claims the benefit of U.S. Provisional Application Ser. No. 63/038,883 filed on Jun. 14, 2020, and U.S. Provisional Application Ser. No. 63/112,128 filed on Nov. 10, 2020, which are incorporated herein by reference.

The present disclosure generally relates to polyisoprene latex and in particular to methods of preparing latex dispersions from natural polyisoprene.

Natural rubber provides products having remarkable resilience, heat resistance and tensile strength. For at least these reasons, tires may be produced from natural rubber rather than synthetic rubber. Out of the four possible isomers of polyisoprene, natural rubber is entirely cis-1,4-polyisoprene. Pure polymer chains of cis-1,4-polyisoprene form aligned polymer chains, resulting in these remarkable properties.

Polyisoprene latex dispersions are useful in the manufacture of dipped products such as wetsuits, condoms, gloves, catheters, angioplasty balloons; to make medical devices or laboratory equipment; for making adhesives for medical and cosmetics uses; as well as in coatings, including those useful for tire applications. The dip molding process in particular relies on using rubber latex dispersions having certain physical and chemical properties to allow for optimization of variables in the process, e.g., dwell time in the latex, leach dip conditions, curing and finishing.

In spite of the long history of natural polyisoprene rubber and latex dispersions comprising cis-1,4-polyisoprene, various industries would benefit from having reliable sources of stable polyisoprene latex dispersions having optimized polymer chain distributions, color, viscosity, and weight percent solids. What is still lacking is a latex process that provides a cis-1,4-polyisoprene latex dispersion having properties optimized for dip-molding.

In accordance with various embodiments of the present disclosure, a process for producing cis-1,4-polyisoprene latex dispersions is described. In various embodiments, the cis-1,4-polyisoprene latex dispersions produced by the methods herein comprise hypoallergenic semi-synthetic guayule latex.

In various embodiments of the present disclosure, a method of producing a cis-1,4-polyisoprene latex dispersion is described. The method is characterized by the steps of dispersing a cis-1,4-polyisoprene rubber cement of a particular weight percent solids into an aqueous surfactant mixture to produce an emulsion, followed by de-solventization of the emulsion to produce an aqueous latex dispersion. In various embodiments, the cement comprises cis-1,4-polyisoprene rubber dissolved in at least one organic solvent. In various embodiments, the de-solventization comprising removing the at least one organic solvent from the emulsion to produce the polyisoprene latex dispersion. The resulting latex dispersion may then be subjected to weight percent solids adjustment, such as by subjecting the latex dispersion obtained by de-solventization to at least one round of centrifugation into phases, phase separation, and dilution of the high solids phase, to adjust solids level to a final targeted weight percent solids.

In various embodiments, a method for producing an aqueous polyisoprene latex comprises: dispersing a cement comprising cis-1,4-polyisoprene rubber dissolved in an organic solvent into an aqueous surfactant mixture to produce a latex emulsion, where said dispersing takes place at a shear rate of greater than 20,000 rad/sec; and removing the at least one organic solvent from the latex emulsion to produce the aqueous polyisoprene latex.

In various embodiments, a method for producing an aqueous polyisoprene latex comprises: extracting guayule plant material with a solvent to obtain a preliminary cement comprising cis-1,4-polyisoprene rubber dissolved in the at least one organic solvent; diluting the preliminary cement with at least one organic solvent to produce a cement; dispersing the cement into an aqueous surfactant mixture to produce a latex emulsion; de-solventizing the latex emulsion to produce an aqueous polyisoprene latex dispersion; and adjusting a weight percent solids level of the aqueous latex dispersion to produce the aqueous polyisoprene latex.

In various embodiments, a method for producing an aqueous polyisoprene latex comprises: extracting guayule plant material with at least one organic solvent to obtain a miscella; fractionating the miscella to obtain a preliminary cement comprising cis-1,4-polyisoprene rubber in the at least one organic solvent; diluting the preliminary cement with at least one organic solvent to produce a cement; dispersing the cement into an aqueous surfactant mixture to produce a latex emulsion; de-solventizing the latex emulsion to produce an aqueous polyisoprene latex dispersion; and adjusting a weight percent solids level of the aqueous latex dispersion to produce the aqueous polyisoprene latex.

In various embodiments, a method for producing an aqueous polyisoprene latex comprises: extracting guayule plant material with a solvent to obtain a miscella; fractionating the miscella to obtain a swollen rubber mass; dissolving the swollen rubber mass in at least one organic solvent to obtain a preliminary cement; diluting the preliminary cement with at least one organic solvent to produce a cement; dispersing the cement into an aqueous surfactant mixture to produce a latex emulsion; and removing the organic solvent latex emulsion to produce the polyisoprene latex dispersion.

Embodiments of the present disclosure are based, at least in part, on the discovery of methods for producing cis-1,4-polyisoprene latex dispersions. According to embodiments of the invention, rubber cements that include rubber obtained from guayule plant material are emulsified, and the latex dispersions are prepared from the emulsion by removal of hydrocarbon solvent. It has been unexpectedly discovered that the manner in which the rubber cement is emulsified leads to advantageous yield without a deleterious impact on polymer properties.

As used herein, the term “natural polyisoprene” refers to a polymer consisting essentially of cis-1,4-polyisoprene. Pure cis-1,4-polyisoprene is found in various trees, shrubs and plants, e.g.,, (i.e., the Amazonian rubber tree),(i.e., the Panama rubber tree), variousvines (, and), various dandelions (i.e.,species of plants), and(guayule shrubs). Although the present disclosure focuses on guayule as the source of the cis-1,4-polyisoprene used in various embodiments of a latex process herein, the processes disclosed herein should not be viewed as being limited to only guayule as the source for cis-1,4-polyisoprene.

As used herein, the term “natural latex” refers to the milky white, viscous sap obtained directly by tapping therubber tree, since this sap naturally flows just under the tree bark. Although this natural latex can be manipulated afterwards to change some of its inherent properties, the material tapped from thetree tends to have far too many allergens present for practical use in dip-molding of medical gloves and condoms. Further, the trees are only indigenous to particular regions of the world outside the United States where access and supply may be an issue. Natural latex emulsions are outside the scope of the present disclosure.

As used herein, the term “semi-synthetic latex” refers to an aqueous dispersion of natural polyisoprene. In other words, although the rubber starting material may be entirely naturally occurring cis-1,4-polyisoprene, the process of forming the latex dispersion involves chemical processes rather than simple tapping of a tree. The present disclosure describes new methods for manufacturing a semi-synthetic latex from natural cis-1,4-polyisoprene obtained from the guayule plant. Guayule is a poor source for natural latex because any latex naturally present in the shrub is trapped intracellularly in the plant cells (not intercellularly), and thus the plant cells must be ruptured to obtain any natural latex, unlike thetree.

As used herein, the term “synthetic latex” refers to an aqueous dispersion of synthetic polyisoprene. Synthetic polyisoprene is prepared by polymerizing isoprene CHin the presence of various catalysts, e.g., in anionic chain or coordinative chain polymerization reactions, optionally as part of emulsion polymerization. Synthetic polyisoprene typically contains one or more of the other three isomers of polyisoprene, namely trans-1,4-, 3,4-addition, and 1,2-addition, although with certain catalysts, (e.g., the Ziegler-Natta catalyst TiCl/Al(i-CH), polyisoprene having >90% cis-1,4-monomers can be synthesized. Synthetic latex emulsions are outside the scope of the present disclosure.

As used herein, the term “cement” refers to a rubber cement, which is a solution comprising polyisoprene dissolved in an organic solvent. In various embodiments, a cement may comprise a single organic solvent (e.g., cyclohexane, acetone), or a blend of solvents as the diluent for the rubber.

As used herein, the term “dispersion” takes on its ordinary meaning in chemistry referring to a homogeneous mixture of fine solid particles in a liquid. Strictly speaking, an “emulsion” is a mixture of fine droplets of liquid in an immiscible liquid, e.g., an oil-in-water emulsion. Although a cis-1,4-polyisoprene aqueous latex is technically a dispersion of fine rubber particles, the terms dispersion and emulsion tend to get interchanged in the art without regard to whether it might be solid particles or liquid droplets finely dispersed in a liquid carrier. Further, an oil may be “dispersed” in water to form an “emulsion.” The methods disclosed herein technically disclose both emulsions and dispersions. For example, a rubber cement, which is a solution of rubber dissolved in an organic solvent, is dispersed into an aqueous solution to produce an emulsion. The resulting emulsion may then be de-solventized to produce an aqueous latex dispersion.

As used herein, the plural “s,” when used in conjunction with a hydrocarbon, e.g., pentanes or hexanes, infers a mixture of isomers of the hydrocarbon, recognizing that some technical grades of low boiling hydrocarbons are mixtures of isomers. Thus, for example, the term “pentanes” indicates a mixture of hydrocarbons comprising n-pentane, iso-pentane and neo-pentane.

The latex dispersions prepared according to embodiments of this disclosure are characterized by including an aqueous dispersion rubber obtained from guayule plant material. This rubber may also be referred to herein as cis-1,4-polyisoprene, natural cis-1,4-polyisoprene, or guayule rubber.

The latex dispersions prepared according to embodiments of this disclosure are characterized by a mechanical stability, as measured according to ASTM D1076-15 (2020), of greater than 650 seconds, alternatively greater than 1000 seconds, in other embodiments greater than 1500 seconds, in still other embodiments greater than 2000 seconds, and further still greater than 2500 seconds.

The latex dispersion prepared according to embodiments of this disclosure are characterized by including rubber having a number average molecular weight (Mn), as measured by gel permeation chromatography using polystyrene standards, of greater than 200 kg/mol (i.e. Daltons), in other embodiments greater than 250 kg/mol, in other embodiments greater than 300 kg/mol, and in other embodiments from about 200 to about 500 kg/mol. In these or other embodiments, the latex dispersions are characterized by including rubber having a weight average molecular weight (Mw), as measured by gel permeation chromatography using polystyrene standards, of greater than 750 kg/mol, in other embodiments greater than 800 kg/mol, in other embodiments greater than 850 kg/mol, and in other embodiments from about 750 to about 1,700 kg/mol. In these or other embodiments, the latex dispersions are characterized by including rubber having a molecular weight distribution (Mw/Mn) of from about 1.5 to about 5 or in other embodiments from about 2 to about 4.

The latex dispersions prepared according to embodiments of this disclosure are characterized by including less than about 1 wt % protein content, which is indicative of low antigenic protein content. The latex dispersions prepared according to embodiments of this disclosure have a total protein content, as measured according to ASTM D5712-2020, of less than or equal to about 200 μg/dm(micrograms per square decimeter of surface area), in other embodiments less than or equal to about 100 μg/dm, in yet other embodiments less than or equal to about 50 μg/dm, and in still other embodiments less than or equal to about 30 μg/dm.

The latex dispersions prepared according to embodiments of this disclosure have a an antigenic protein content, as measured according to ASTM D6499-2018, of less than or equal to about 2 μg/dm, in other embodiments less than or equal to about 1 μg/dm, in yet other embodiments less than or equal to about 0.5 μg/dm, and in still other embodiments less than or equal to about 0.25 μg/dm.

The latex dispersions prepared according to embodiments of this disclosure can be characterized by their particle size, which can be measured by employing scanning transmission electron microscopy with a HAADF detector using dark field and bright field images. In one or more embodiments, the latex dispersions prepared according to embodiments of this disclosure have a mean particle size that is greater than 200 nm, in other embodiments greater than 300 nm, and in other embodiments greater than 400 nm. In these or other embodiments, the latex dispersions prepared according to embodiments of this disclosure have a mean particle size that is less than 2000 nm, in other embodiments less than 1800 nm, and in other embodiments less than 1500 nm. In one or more embodiments, the latex dispersions prepared according to embodiments of this disclosure have a mean particle size of from about 200 to about 2000 nm, in other embodiments from about 300 to about 1800, and in other embodiments from about 400 to about 1500 nm. In one or more embodiments, the latex dispersions prepared according to embodiments of this disclosure have a particle size mode that is greater than 40 nm, in other embodiments greater than 100 nm, in other embodiments greater than 150 nm, and in other embodiments greater than 200 nm. In these or other embodiments, the latex dispersions prepared according to embodiments of this disclosure have a particle size mode that is less than 1000 nm, in other embodiments less than 900 nm, and in other embodiments less than 750 nm. In one or more embodiments, the latex dispersions prepared according to embodiments of this disclosure have a particle size mode of from about 40 to about 1000 nm, in other embodiments from about 150 to about 900, and in other embodiments from about 200 to about 750 nm.

The latex dispersions prepared according to embodiments of this disclosure can be characterized by an advantageously low resin content. The skilled person understands that latex dispersions derived from the guayule plant contain guayule resin, which includes monoterpenes, triterpenes (Argentatin A, B and C), sesquiterpene compounds (Guayulin A and B) and fatty acids (as free fatty acid, monoglycerides, diglycerides, triglycerides, or a combination thereof). The skilled person also understands that these resins have a plasticizing effect on natural rubber, and fatty acid triglycerides can facilitate oxidative degradation of the latex. The latex dispersions prepared according to embodiments of this disclosure have a resin content, as measured according GPC using polystyrene standards, of less than or equal to of about 2.0%, in other embodiments less than or equal to about 1.5%, and in alternative embodiments less than or equal to about 1.2 wt %.

The latex dispersions prepared according to embodiments of this disclosure can be characterized by an advantageously low content of molecules having a molecular weight of less than 1000 g/mol, which can be determined by using GPC with polystyrene standards. In one or more embodiments, the latexes include less than 7 wt %, in other embodiments less than 4 wt %, and in other embodiments less than 3 wt % of molecules having a molecular weight of less than 1000 g/mol.

The latex dispersions prepared according to embodiments of this disclosure are devoid or substantially devoid of thickeners, where substantially devoid refers that amount or less that does not have an appreciable impact on the latex or its use. The skilled person understands that thickeners that are used in latex dispersions include casein, alginates and cellulose. In one or more embodiments, the latex dispersions of this disclosure include less than 2 wt %, in other embodiments less than 0.5 wt %, and in other embodiments less than 0.1 wt % thickeners.

As indicated above, the latex dispersions according to embodiments of this disclosure are generally prepared by dispersing a rubber cement into an aqueous surfactant mixture. The rubber cement includes rubber extracted from guayule plant material. Processes for preparing the latex dispersions can be described with reference to. The starting point of the process may depend on the starting material. For example, if beginning with guayule plant material, the process may begin with extracting the plant. The steps of extracting plant material may vary depending on whether the cement is produced directly from guayule plant material or if a swollen rubber mass is obtained that has to be diluted with an organic solvent to provide the rubber cement. Where the cement is provided, the step or steps of extracting plant material may be eliminated.

As shown in, a methodfor producing a latex dispersion in accordance with the present disclosure generally includes providing a cement for dispersion, which can include an optional stepof extracting guayule plant material with an organic solvent to obtain a miscella. In an optional step, the miscella is fractionated to produce a preliminary cement. In an optional step, the preliminary cement can be diluted with an organic solvent to produce a cement having suitable rubber solids content for dispersion. Alternatively, in an optional step, the cement is desolventized to produce a desolventized rubber. The desolventized rubber can be re-dissolved in a solved to from a rubber cement that requires further dilution in stepor a cement having suitable rubber solids content for dispersion. In either pathway, the rubber cement can be optimized to an appropriate rubber solids level, resin, and bagasse levels, that is suitable for dispersion.

With continued reference to, a stepincludes the separate preparation of an aqueous surfactant mixture by dissolving a surfactant into water and adjusting the pH to with an alkali (i.e. a basic, ionic salt of an alkali metal or an alkaline earth metal). Stepis followed by a stepthat includes dispersing the rubber cement and the aqueous surfactant mixture to produce an emulsion (i.e. a composition where the cement is dispersed in the aqueous phase). Formation of the emulsion is optionally followed by an optional stepthat includes the optional addition of an antioxidant to the latex emulsion. Then, the emulsion is subjected to a stepthat includes desolventizing the emulsion to produce an aqueous latex dispersion. Lastly, stepincludes adjusting the final rubber solids level in the aqueous latex dispersion.

As indicated above, the methods of this disclosure optionally include methods for providing a preliminary cement by extracting guayule plant material. In various embodiments, extraction of guayule plant material may proceed by solvent extraction methods and may include any combination of regular solvent extraction and/or multistage fractionation, including counter-current multistage extraction and/or counter-current multistage fractionation processes. In various embodiments, guayule shrubs are harvested and the plant material dried to leave between about 5 wt % and 25 wt % moisture. With this processing, less than about 15%, or less than about 10% by weight of leaves may still remain on the dried shrubs.

In various embodiments, solvent extraction of guayule plant material may include chopping, grinding, macerating or otherwise breaking up dried guayule stems (optionally with <10-15 wt % of remaining leaves) in a solvent mixture including hydrocarbon solvent and a polar organic solvent to produce a miscella. The miscella can then be fractionated to obtain the preliminary cement. In various embodiments, the solvent mixture used for the regular extraction can include about 30 wt % acetone and 70 wt % hexanes.

In various embodiments, the step of fractionating the miscella includes adding a polar organic solvent to the miscella. In various embodiments, the step of fractioning the miscella may include multistage countercurrent fractionation with concomitant addition of a polar solvent (e.g. acetone) countercurrent to the flow of the miscella. At the end of the fractionator, the preliminary cement may include from about 10 wt % to about 25 wt % cis-1,4-polyisoprene rubber in solvent (e.g. a mixture of iso-hexane and acetone).

Methods for extracting guayule plant material to provide a preliminary cement are known in the art as described in U.S. Pat. Nos. 9,315,589B2, 9,637,562B2, 10,316,110B2, 11,028,188B2, 9,611,334B2, 9,890,262B2, 10,626,194B2, 10,112,123B2, 10,717,021B2, and 10,843,103B2, which are incorporated herein by reference.

In various embodiments, the preliminary cement from the fractionating step may include from about 0.1 wt % to about 8.0 wt % resin, in other embodiments from about 1 to about 5 wt %, and in other embodiments from about 1.5 to about 4 wt % resin based upon the total solids content of cement. In various embodiments, the preliminary cement includes less than 8.0 wt % resin, in other embodiments less than 6.0 wt % resin, in other embodiments less than 4.0 wt % resin, and in other embodiments less than 3.0 wt % resin based upon the total solids content of the cement. As those skilled in the art will appreciate, the amount of resin present in the preliminary cement can be determined by GPC using polystyrene standards.

In these or other embodiments, the preliminary cement includes from about 0.01 wt % to about 1.0 wt. % ash, in other embodiments less than 1.0 wt %, in other embodiments less than 0.5 wt. %, and in other embodiments less than 0.25 wt % as based on the total solids content of preliminary cement. As those skilled in the art will appreciate, the amount of ash present in the preliminary cement can be determined by various thermal decomposition mass analysis. For example, weighed samples can be heated in covered crucibles (e.g. within a muffle furnace) at 750° C. for 20 minutes, then heated uncovered at 750° C. for three hours, and weighed. Analyses can also be made by Thermogravimetric analysis (TGA). In one such method, a sample is ramped at a rate of 20° C./min from ambient under nitrogen and then held at 250° C. for 20 minutes, then ramped at a rate of 20° C./min to 600° C., nitrogen is replaced by air and held for 10 minutes at 600° C., and then ramped to 750° C. and held for five minutes, at which time the sample is weighed and ash calculated based upon residual weight.

In various embodiments, the method for producing a polyisoprene latex dispersion includes extracting guayule plant material in a solvent mixture including at least one hydrocarbon solvent and at least one polar organic solvent to produce a miscella; fractionating the miscella to obtain a preliminary cement including cis-1,4-polyisoprene rubber in at least one organic solvent; diluting the preliminary cement including cis-1,4-polyisoprene rubber to a cement including cis-1,4-polyisoprene rubber dissolved in at least one organic solvent; dispersing the cement into an aqueous surfactant mixture to produce an emulsion; and removing the at least one organic solvent from the emulsion to produce the polyisoprene latex dispersion. In various embodiments, these steps may include combinations of the various elements set forth and discussed herein. In various embodiments, the step of fractionating further includes multistage countercurrent fractionation with concomitant addition of at least one polar organic solvent to produce a preliminary cement including cis-1,4-polyisoprene rubber in at least one organic solvent. In various embodiments, multistage countercurrent fractionation includes addition of acetone. In various embodiments, fractionation of the miscella includes precipitation of a swollen rubber mass from the miscella by addition of at least one polar organic solvent such as acetone, and re-dissolving the swollen rubber mass in at least one organic solvent to produce the preliminary cement.

As indicated above, the process may include the optional step of diluting the preliminary cement to a cement for dispersion. In one or more embodiments, the cement for dispersion includes a final solids level of from about 5 wt % to about 25 wt % cis-1,4-polyisoprene rubber. In various embodiments, the preliminary cement is diluted to a cement including less than or equal to 20 wt % cis-1,4-polyisoprene rubber, in other embodiments less than less than or equal to 15 wt % cis-1,4-polyisoprene rubber, and in other embodiments less than or equal to 10 wt % cis-1,4-polyisoprene rubber. In various embodiments, the preliminary cement is diluted to a cement including from about 5 wt % to about 10 wt % cis-1,4-polyisoprene rubber, in other. In various embodiments, the step of diluting the preliminary cement includes diluting the preliminary cement with hexanes (e.g., iso-hexane), or diluting the preliminary cement with a blend of solvents (e.g. a blend of iso-hexane, cyclohexane and acetone).

In one or more embodiments, the preliminary cement is de-solventized. Practice of these embodiments of the invention are not necessarily limited by the methods used to remove solvent from the preliminary cement. The skilled person will appreciate that several methods can be used to remove the solvent from the preliminary cement and thereby provide a de-solventized rubber, which may also be referred to as a dried rubber. In one or more embodiments, the de-solventized rubber includes less than 5 wt %, in other embodiments less than 2 wt %, and in other embodiments less than 0.5 wt % solvent (e.g. less than 0.25 weight percent volatile organic compounds).

According to these embodiments, de-solventized rubber can then be dissolved in a solvent to form the cement for dispersing. For example, the de-solventized rubber can be dissolved in a mixture of non-polar and polar organic solvent to produce a rubber cement usable in the dispersion process. As with other embodiments, the solids content of the cement can be further adjusted with solvent to produce a cement usable in the dispersion process. Those skilled in the art will appreciate that the step of de-solventizing the preliminary cement and then later dissolving the de-solventized cement allows for storage, shipment, and handling of the rubber obtained from guayule (e.g. extraction and fractionation) in the absence of solvent (e.g. volatile organic compounds) and then subsequently forming the cement useful for dispersing.

In various embodiments, the cement prior to dispersion includes from about 5 wt % to about 25 wt % cis-1,4-polyisoprene rubber. In various embodiments, the cement prior to dispersion comprises less than or equal to about 20 wt % cis-1,4-polyisoprene rubber, in other embodiments less than or equal to about 15 wt % cis-1,4-polyisoprene rubber, in other embodiments less than or equal to about 10 wt % cis-1,4-polyisoprene rubber, and in other embodiments from about 5 wt % to about 10 wt % cis-1,4-polyisoprene rubber.

In various embodiments, the cement includes a hydrocarbon solvent, which includes non-polar and polar hydrocarbon solvents. In particular embodiments, the cement includes a mixture of non-polar and polar solvents (which may also be referred to as polar organic solvents).

In one or more embodiments, the non-polar hydrocarbon solvent may include Cto Cstraight chain hydrocarbons, Cto Cbranched chain hydrocarbons, Cto Ccyclic hydrocarbons, Cto Caromatic hydrocarbons, and mixtures thereof. In various embodiments, particular combinations of solvents provide an azeotropic mixture, thus simplifying removal of the solvents at a later stage.

In particular embodiments, the non-polar hydrocarbon solvent includes a pentane such as cyclopentane, n-pentane, iso-pentane, neo-pentane, and mixtures thereof. In these or other embodiments, the non-polar hydrocarbon solvent includes a hexane such as n-hexane, iso-hexane, 3-methylpentant, 2,3-dimethylbutane, neo-hexane, cyclohexane, and mixtures thereof. In these or other embodiments, the non-polar hydrocarbon solvent includes a Cto Caromatic hydrocarbon such as benzene, toluene, o-xylene, m-xylene, p-xylene, ethylbenzene, 1,2,3-trimethylbenzene, 1,2,4-trimethylbenzene, mesitylene, 2-ethyltoluene, 3-ethyltoluene, 4-ethyltoluene, and mixtures thereof.

In these or other embodiments, the hydrocarbon solvent includes a polar organic solvent such as acetone, C-Calcohols, C-Cdiols, and mixtures thereof.

In exemplary embodiments, the solvent in the cement prior to dispersion includes pentanes, and/or hexanes, and/or acetone, and/or a mixture of acetone and hexanes, and/or iso-hexane, and/or acetone and iso-hexane, and/or iso-hexane, cyclohexane and acetone.

In one or more embodiments, the solvent of the cement for dispersing into the aqueous surfactant mixture is characterized by the weight ratio of polar solvent to non-polar solvent. This can be quantified based upon the weight of polar solvent present relative to the total weight of polar and non-polar solvent. In one or more embodiment, the cement for dispersing into the aqueous surfactant mixture includes from about 20 to about 55 wt %, in other embodiments from about 30 to about 50 wt %, and in other embodiments from about 35 to about 45 wt % polar solvent, based on the total weight of the solvent (i.e. the total weight of polar and non-polar solvent combined). In one or more embodiments, the cement for dispersing into the aqueous surfactant mixture includes greater than 20 wt %, in other embodiments greater than 25 wt %, and in other embodiments greater than 30 wt % polar solvent based on the total weight of the solvent.

As indicated above, the process includes preparing a aqueous surfactant mixture. In various embodiments, the aqueous surfactant mixture includes a surfactant in water. In various embodiments, the total amount of surfactant present in the aqueous surfactant mixture may be from about 0.01 wt % to about 20.0 wt %. In various embodiments, the surfactant may include anionic surfactants, nonionic surfactants, cationic surfactants, amphoteric surfactants, and mixtures thereof.

Anionic surfactants for use herein include, but are not limited to, alkyl sulfates, also known as alcohol sulfates. These surfactants have the general formula R—O—SOM, where R is from about 10 to 18 carbon atoms, and M represents an alkali metal such as sodium or potassium or ammonium, and these materials may also be denoted as sulfuric monoesters of C-Calcohols, examples being sodium decyl sulfate, sodium palmityl alkyl sulfate, sodium myristyl alkyl sulfate, sodium dodecyl sulfate, sodium tallow alkyl sulfate, sodium coconut alkyl sulfate, and mixtures of these surfactants, or of C-Coxo alcohols, and those monoesters of secondary alcohols of this chain length. Also useful are the alk(en)yl sulfates of said chain length which contain a synthetic straight-chain alkyl radical prepared on a petrochemical basis, these sulfates possessing degradation properties similar to those of the corresponding compounds based on fatty-chemical raw materials. From an emulsification standpoint, C-C-alkyl sulfates, C-C-alkyl sulfates, and also C-Calkyl sulfates, are all useful. For example, sodium lauryl sulfate from the Stepan Company sold under the trade name of Polystep® can be used.